FULLTEXT Indexes
A special kind of index, the FULLTEXT index, helps InnoDB deal with queries and DML operations involving text-based columns and the words they contain. These indexes are physically represented as entire InnoDB tables, which are acted upon by SQL keywords such as the FULLTEXT clause of the CREATE INDEX statement, the MATCH() ... AGAINST syntax in a SELECT statement, and the OPTIMIZE TABLE statement. For usage information, see , "Full-Text Search Functions".
You can examine FULLTEXT indexes by querying tables in the INFORMATION_SCHEMA database. You can see basic index information for FULLTEXT indexes by querying INNODB_SYS_INDEXES. Although InnoDB FULLTEXT indexes are represented by tables, which show up in INNODB_SYS_TABLES queries, the way to monitor the special text-processing aspects of a FULLTEXT index is to query the tables INNODB_FT_CONFIG, INNODB_FT_INDEX_TABLE, INNODB_FT_INDEX_CACHE, INNODB_FT_DEFAULT_STOPWORD, INNODB_FT_INSERTED, INNODB-FT-DELETED, and INNODB_FT_BEING_DELETED.
InnoDB FULLTEXT indexes are updated by the OPTIMIZE TABLE command, using a special mode controlled by the configuration options innodb_ft_num_word_optimize and innodb_optimize_fulltext_only.